1. Field of the Invention
The present invention relates to an average current detector circuit.
2. Description of the Related Art
A switching power supply device, which switches on/off its switching element in response to a control pulse to flow a current intermittently through a coil, is known. This kind of device obtains the average value of the current flowing through the coil in order to have control over the on/off of its switching element. For example, Unexamined Japanese Patent Application KOKAI Publication No. 2003-111485 discloses a sample/hold circuit which obtains the average current across a coil by sampling a voltage corresponding to the current flowing through the coil, synchronously at the center point of a control pulse.
However, it is difficult to locate the center point of a control pulse in real-time. Particularly, in case of PWM (Pulse Width Modulation) control, etc., since the width of a control pulse changes constantly, it is hard to spot the center point of the control pulse accurately. The sample/hold circuit fails to obtain the average current accurately. As a result, the sample/hold circuit cannot control the voltage to be output therefrom accurately.